Answer: a.       If the unwell person in question is one’s parent, Kaddish can be said even when there is a doubt, as explained in the Be’er Heitev, Orech Chaim 132, 105,) but this is in the event that one’s mother is no longer alive, so that there will not be a concern that she will remarry based on the ‘evidence’ of Kaddish being said for her husband, as mentioned in certain sources. b.       If the absent person is single and there is no concern that his wife will be allowed to marry on the basis of Kaddish being said for him, there are differing opinions in the Halachic sources, the conclusion being that it is permissible to say Kaddish. It is recommended to recite mishnayot in any case, for that can only help.